This invention is directed to decks and other outside constructions, and in particular to a hollow flanged joist which can be used in place of wooden joists in framing.
The majority of decks built in North America are constructed from wood, this includes the framing as well as the decking surface. However, with age and exposure to moisture, wood can split, warp, splinter and rot. These effects are most apparent on the horizontal decking surfaces where water can collect, especially if the deck boards become cupped. Recently, a number of manufacturers have started offering profiles made from moisture resistant materials which can be used as an alternative to wood decking in the construction of decks. These non-wood decking products, such as those produced by Trex Company Inc., Winchester, Va., and Advanced Environmental Recycling Technologies Inc. (AERT), Springdale, Ariz., are said to offer a number of advantages over wood, particularly relating to the moisture resistance of the materials used in their manufacture.
While there are a growing number of manufacturers of these non-wood decking products, most of these manufacturers recommend against using their products as structural members, such as joists. Typically, the manufacturers of the non-wood decking products recommend using wood to construct the structure on which the non-wood decking product is installed. This results in a decking surface which may have a lifetime guarantee, while the wooden structure supporting it is still prone to moisture damage and may need replacement if the damage is severe enough. The effects of moisture on the framing can be minimized by using naturally moisture resistant wood species such as cedar or redwood, which are usually sold at a substantial premium to less moisture resistant species. A more economical solution has been to use pressure treated lumber as the framing members with the non-wood decking products. However, the effect of the pressure treating will decrease over time as the chemicals leach out of the wood. As such, using moisture resistant wood species and pressure treated lumber will delay the decay of the wood, but it will not prevent splitting, warping and splintering of the wood, which is caused by repeated cycles of the wood getting wet and drying out and can significantly weaken the structural members.
In February of 2002, the United States Environmental Protection Agency announced a phase-out of chromated copper arsenate (CCA) treated lumber by the treated lumber industry. At the time, CCA treated lumber accounted for over 80% of pressure treated lumber sold in North America. The phase out was the result over the concerns over the toxicity of the CCA and the fact that it can readily leach out from lumber and contaminate nearby soil. Other chemical preservatives are available with the most likely successor to CCA being alkaline copper quaternary (ACQ), which is substantially more expensive than CCA, and will result in higher treated lumber prices. These various chemical formulations used in pressure treating typically act as fungicides which enhance the moisture resistance of the wood by killing fungi which can lead to rot and decay. However, according to the Canadian Environment Ministry, all chemical wood preservatives are classified as pesticides as they achieve decay control as a result of their significant toxicity, and that while the potency of the various preservatives varies, all are poisonous to some degree and are potentially hazardous to humans and other forms of life. In addition, as a result of increased demand, the phase out of CCA treated lumber has resulted in increased prices for lumber from moisture resistant wood species such as cedar.
Currently, there is only one type of product which is being promoted for use as structural members to replace wood framing in building decks, and that is glass fiber reinforced high density polyethylene (HDPE) plastic lumber, such as that produced by US Plastic Lumber Ltd., Boca Raton, Fla. These products are usually solid and mimic the sizes and shape of standard lumber profiles (i.e. 2xc3x976, 2xc3x978, etc.). However, as a result of the significantly higher density of these products, they are substantially heavier than wood of the same size. In addition, as the mechanical properties (particularly the flexural modulus) of these products are typically lower than wood, they cannot span as far as similarly sized wood joists. As a result of the glass fiber content, these products can be difficult to cut and drill and can quickly dull saw blades and drill bits. Finally, because of the relatively high cost of the glass fiber reinforcement, the cost of these products can be many times that of wood even when they are produced using recycled HDPE.
One way to reduce the cost of a joist is to reduce the amount of material used in its production by concentrating the material used to where the most stress is experienced. In a joist, which is typically exposed to bending loads, the most stress is at the top and bottom surfaces of the joist. It is well known that I-shaped flanged beams are very efficient at resisting bending loads as are typically seen in construction applications and have a greater strength to weight ratio than similarly sized solid beams because the material of the beam is concentrated where the greatest stresses are experienced. Another way to reduce the weight of a beam is to make it hollow rather than solid. This offers two advantages. First, less material is used, which reduces the cost. Second, by reducing the weight of the beam it reduces the load on any support structure for the beam.
Therefore it would be desirable to have a product which could be used to replace untreated lumber, pressure treated lumber, cedar and redwood in framing for decks which use moisture resistant non-wood decking products. Preferably the product has the same moisture resistant characteristics of the non-wood decking products. Preferably it should be easy to work with (i.e. have the workability of wood), be easy to install and, where possible, offers additional features. In order to address the concerns regarding the weight, the flexibility and the cost of currently available non-wood products sold for use as structural framing members for decks, preferably the product makes use of the structural advantages of a flanged beam configuration and the weight savings of a hollow profile.
The invention involves a hollow flanged joist, produced via extrusion or pultrusion, which is intended to be used as a framing member in the construction of decks or other exterior structures and has a shape substantially that of a I-shaped beam.
The hollow flanged joist consists of a center web section and top and bottom flange sections. The center web section has two generally parallel center vertical webs and at least one center horizontal web. The center horizontal web extends between the center vertical webs and is generally perpendicular thereto. The center web section has a top end and a bottom end. The top flange section extends outwardly and generally perpendicularly from the top end of the center web section on each side thereof. The top flange section has a horizontal flange end web, a pair of vertical flange side webs extending downwardly from the ends of the flange end web and a pair of horizontal flange inner webs. One of the pair of horizontal flange inner webs extends inwardly from the inner end of each flange side web and connects to the adjacent center vertical web. The bottom flange section extends outwardly and generally perpendicularly from the bottom end of the center web section on each side thereof. The bottom flange section has a horizontal flange end web, a pair of vertical flange side webs extending upwardly from the ends of the flange end web and a pair of horizontal flange inner webs. One of the pair of horizontal flange inner webs extends inwardly from the inner end of each flange side web and connects to the adjacent center vertical web.
Optionally the top and bottom flange sections may also each have a number of flange support webs which can extend between the respective flange end web and the adjacent outermost center horizontal web or the flange inner webs. In a preferred embodiment, the flange support webs are positioned such that they are in line with the center vertical webs.
Preferably the hollow flanged joist is made from a moisture resistant material such as a thermoplastic or thermosetting resin which may or may not contain reinforcing fillers whose purpose is to increase the strength and stiffness of the profile. Further, the choice of the moisture resistant material should yield a product with sufficient strength and rigidity as to be a cost effective replacement for wood framing members.
Preferably, the hollow flanged joist is dimensioned such that it can easily be substituted for the wood framing members it is meant to replace. Further, the design should allow for easy joining of the hollow flanged joists in framing a deck and incorporate features which increase the functionality of the product by indicating the preferred location for fasteners and the like.
In another preferred form, the hollow flanged joist will be designed such that the hollow channels are sized so that reinforcing inserts can be introduced into the hollow flanged joist to increase the strength and stiffness of the profile.
Other features and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments and illustrate various features and designs thereof.